This N10-009 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security analyst discovers that an unauthorized device is sending forged ARP replies to poison the ARP caches of other devices on the network. Which security feature should be implemented on the switches to prevent this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Dynamic ARP Inspection
Dynamic ARP Inspection (DAI) validates ARP packets on a per-interface basis by intercepting all ARP requests and replies and verifying that they match entries in the DHCP snooping binding table. If an ARP reply contains a forged IP-to-MAC mapping, DAI drops the packet, preventing ARP cache poisoning. This directly stops the described attack where an unauthorized device sends forged ARP replies.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Port security
Why it's wrong here
Port security limits the number of MAC addresses on a port but does not validate ARP packets.
✗
DHCP snooping
Why it's wrong here
DHCP snooping filters DHCP messages and builds a binding table, but does not directly inspect ARP traffic.
✓
Dynamic ARP Inspection
Why this is correct
DAI uses the DHCP snooping binding table to validate ARP packets and drop spoofed ones.
Related concept
Read the scenario before looking for a memorised answer.
✗
STP BPDU guard
Why it's wrong here
BPDU guard protects the spanning tree topology by shutting down ports that receive BPDUs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between DHCP snooping (which builds the trust database) and Dynamic ARP Inspection (which uses that database to filter ARP traffic), leading candidates to mistakenly choose DHCP snooping as the direct solution for ARP spoofing.
Detailed technical explanation
How to think about this question
DAI relies on the DHCP snooping binding database, which maps each client’s IP address to its MAC address, VLAN, and switchport. When an ARP reply arrives, DAI compares the sender IP and MAC against this database; if no match exists, the packet is dropped. In environments without DHCP (static IPs), DAI can use ARP ACLs to define trusted mappings, but the default behavior requires DHCP snooping to be enabled first.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Dynamic ARP Inspection — Dynamic ARP Inspection (DAI) validates ARP packets on a per-interface basis by intercepting all ARP requests and replies and verifying that they match entries in the DHCP snooping binding table. If an ARP reply contains a forged IP-to-MAC mapping, DAI drops the packet, preventing ARP cache poisoning. This directly stops the described attack where an unauthorized device sends forged ARP replies.
What should I do if I get this N10-009 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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